This application claims the priority of German application 198 34 832.6, filed in Germany on Aug. 1, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for changing the At rotational position of a shaft relative to a drive wheel, especially of a camshaft of an internal combustion engine with an adjusting device that can be pressurized hydraulically and which includes two pressure chambers that act against one another, said chambers being formed by an inner part connected with the shaft and a compartmented wheel of the adjusting device that is connected with the drive wheel, with at least one depression in the wall area of each of the pressure chambers.
A device of this kind is known for example from European Patent Document EP 0 781 899 A1. This document describes a device for changing the rotational position of the camshaft of an engine, with the camshaft being connected nonrotatably with an inner wheel, said wheel having vanes arranged radially and dividing the associated compartments of a compartmented wheel into two pressure chambers each that act against one another. These pressure chambers are pressurized hydraulically by a control valve. Depending upon the pressurization, the inner wheel is rotated relative to the compartmented wheel. The walls of the compartmented wheel that extend radially are provided in the vicinity of their radial outer sides with depressions provided to receive dirt particles that are introduced by the pressure medium into the pressure chambers. The dirt particles contained in the pressure medium, depending on the rotational direction of the camshaft, as a result of the accelerations acting on them and of their inertia, accumulate primarily in one of the two depressions. This depression is the one located to the rear relative to the rotational direction. The dirt particles located on the front side of each vane or rib of the inner part can be pressed by their relative movement into the front depression of the compartmented wheel, but because of their inertia they do not remain there. Therefore, with such an adjusting device, there is the danger that smaller dirt particles in particular in the sealing gap between the vane and the rib, will penetrate the compartmented wheel and result in considerable wear and a sealing effect that decreases over time. In addition, the penetration of dirt particles into this sealing area can lead to a sharp increase in friction. This would result in a much higher pressure requirement to achieve a sufficiently rapid adjustment. Moreover, such depressions in the walls between the adjoining compartments require relatively thick walls and are located in an area that is unfavorable from the standpoint of stress. The considerable wall thickness required by the depressions consequently reduces the width of the adjoining compartments in the circumferential direction of the adjoining compartments, so that the adjustment angle is reduced overall.
On the other hand, a goal of the invention is to improve the adjusting device of the type generally described above in such fashion that dirt particles can settle out of the pressure medium in non-critical areas of the pressure chambers without the danger of increased friction and/or increased wear in the area of the sealing surface.
This goal is achieved according to preferred embodiments of the invention by providing a device of the above described type wherein the depressions are formed in a radially external circumferential surface of the compartmented wheel. By locating the depressions in the radially external circumferential surface, the dirt particles that collect in the depressions under the influence of acceleration, due to their inertia, are prevented from again penetrating the sealing surface between the vane or rib and the circumferential surface of the compartmented wheel. By locating the depressions in the circumferential surface, moreover, the thickness of the radial compartment walls is not reduced so that the maximum possible adjustment angle is retained.
If a plurality of depressions are machined into the circumferential surface in each pressure chamber around the circumference, in an especially advantageous manner the distance can be reduced that dirt particles must travel along the circumferential surface until they can settle in a depression.
Especially simple machining of the compartmented wheel and a relatively large volume to receive the dirt particles are obtained when the depressions extend in the axial direction over the entire length of the pressure chamber.
Despite the location of the depressions in the circumferential area and consequently in the vicinity of the sealing surface with the adjoining rib of the inner part, a good seal can be ensured if the width of the depressions, viewed in the circumferential direction, is chosen so that in each case at least two depressions are sealed by the adjoining end of a rib. The part of the circumferential surface located between the depressions therefore has a sufficient sealing length for the operation of the adjusting device.
An especially good sealing effect at the circumferential surface is achieved if the width of the depressions and/or of the spaces between the depressions is less than 20 percent of the width of the adjoining rib.
An even further improved sealing effect is achieved when the width and/or the distance between the depressions is less than 10 percent of the width of the adjoining rib.
A good and rapid collection of dirt particles with a simultaneous high sealing effect is achieved when the width of the depressions is approximately 0.5 to 1 mm. The depth of the depressions in the radial direction is preferably in the range between 0.2 and 0.5 mm. The depressions can then have a square cross section for example. A design that is especially favorable from the manufacturing standpoint is obtained when the depressions have an approximately semicircular cross section with a slightly conical opening area to the inner chamber.
A compartmented wheel with depressions on its circumferential surface can be manufactured in an especially advantageous and economical fashion as a sintered part. The depressions to receive the dirt particles can then be formed by the sintering process itself. The machining of the circumferential surface following the sintering process is then possible without additional effort or additional cost, as in the case of parts without depressions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.